Coke-making is a carbonization process of coal suitable as a reducing agent for iron oxide at elevated temperatures. The resultant carbonized material is called coke. To use coke for reducing iron oxide, certain physical, mechanical, and chemical properties are desirable. Both moisture and volatile hydrocarbons are removed from coal and unique mechanical and physical properties are formed. There are two types of conventional coke-making processes: (1) recovery coke-making, and (2) non-recovery coke-making. While the recovery coke-making process (all volatile hydrocarbons are recovered) has been a dominant process for the last fifty years, the cost of environmental controls and operations have made the process economically non-competitive. Since new non-recovery processes recover heat from burning the volatile hydrocarbons and convert it to power, these new non-recovery processes are now emerging as the main coke-making processes in the industry.
Conventional sulfur-reducing technologies related to conversion of coal into metallurgical coke can be classified into two general categories: (1) removal of sulfur in the coal before the coke oven, and (2) removal of sulfur-containing gases in the flue gas of the coke oven. Technologies belonging to the first category include floatation (selective floating of the sulfur-containing compounds) and coal washing. Technologies belonging to the second category include spraying chemical compounds into the flue gas and dry/wet scrubbing.